Electricity can be generated at stationary power plants from hydrogen-enriched raw fuel upon oxidation in a fuel cell stack wherein a plurality of fuel cells are bundled together. Control systems that monitor flow through and output from reformers and fuel cell stacks can facilitate power plant management during power output fluctuations, for example buffer systems in the form of batteries and/or super-capacitors, may be employed to safeguard the power plant components from such transients.
Maintenance of electron flow through a fuel cell circuit can be achieved by ensuring a continued presence of hydrogen on the anode side where it dissociates into protons and electrons in the presence of an anode catalyst. In the absence of hydrogen, the integrity of the fuel cell may be compromised. Thus in one approach to power plant management, a large anode inventory of hydrogen is ensured by the usage of large fuel cell stacks. However, the inventors have herein recognized this may generate a need for large amounts of fuel and corresponding large areas to house the fuel.
Since the power, and therefore the current, drawn from a fuel cell impacts the extent of losses incurred, and consequently the efficiency of the fuel cell, it is also desirable to maintain the power output from a fuel cell stack. Additionally, fuel cell activation losses can contribute to output voltage decreases. Thus, in another approach to power plant management, a control system is incorporated to adjust reformer capacity in response to the current drawn from the fuel cell stack. Adjustments in reformer capacity by variation of input raw fuel and steam amounts allows for adjustments in the level of hydrogen-enriched fuel that enters the fuel cell stack. However, the inventors herein have also recognized a disadvantage with such an approach. Specifically, the response time involved in the adjustment of the reformer's water and fuel flow rates, adjustment of steam air blower speeds, and regulation of system temperature levels, can often be longer than desired. Late response times can lead to component damage due to a temporary insufficiency in the levels of hydrogen on the anode side of the fuel cell, even if sufficiently large amounts of fuel storage are utilized. The damage may be exacerbated in case of transient fluctuations.
In one approach, the above issues may be addressed by a method of operating a power generating system including a fuel cell coupled to an electrical buffer, where the fuel cell is further coupled to a steam reformer. The method may comprise adjusting operation of the reformer based on a voltage affected by the electrical buffer while maintaining a steam to carbon ratio of the reformer to control charging of the electrical buffer by the fuel cell. For example, the method may comprise compensating for increased power demand by providing current from the electrical buffer before the fuel cell current is increased by the adjustment of the reformer.
In this way, by adjusting the reformer responsive to the voltage, the reformer can lead the system in response to voltage disturbances. Thus, an electrical buffer may be used to compensate the demand during transient conditions (e.g., for ancillary devices such as pumps, blowers, etc. to react), rather than relying on a large buffer of fuel, for example, to reduce the likelihood of insufficient fuel at the anode.
It should be understood that the above description is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.